1. Field of the Invention
The present invention is directed generally to non-aqueous electrochemical cells or batteries having a plurality of sandwiched electrode layers and, more particularly, to an improved cell separator construction which allows reliable testing with respect to locating high or low resistance shorts which may develop in the cells during cell construction.
2. Description of the Related Art
Bipolar, multi-electrode layer cells of cylindrical construction are typical electrochemical cells of the class of interest in the present invention. They include a plurality of stacked battery components exposed to an electrolyte solution within the elongated housing of the cell which may be of metal or of a polymeric or plastic or prismatic material and is normally cylindrical in shape. The battery components are arranged in a concentric sandwich construction within the housing in which a plurality of metal anode structure layers and a plurality of carbon or other cathode electrode structures are arranged alternately with the electrode structures spaced by a plurality of separator membranes. The plurality of metal anode structures, each of which may be a lithium grid pressed into a nickel foil backing, generally employed within the cell may be arranged to be joined in parallel and in direct physical contact with the internal wall of the housing to form one pole of the bipolar cell. The plurality cathode structures, which may be carbon electrodes pressed into nickel grid cathode collector plates, are likewise joined to a second lead which is conducted outside the cell through an insulated connection to form a pin terminal on the top of the battery. A plurality of anode and cathode layers are normally pressed together in stacked fashion to form an extremely thin, high energy density composite cell. Because of the dense nature of the o cell construction and the relatively large area between the plurality of sets of oppositely charged cell plates, it is important that the integrity of the separators be consistent throughout to prevent internal shorts from robbing needed battery power.
In this regard, it has heretofore been somewhat difficult to ascertain the integrity of typical bipolar battery construction in the form of locating high or low resistance shorts which might occur between layers of the stacked electrodes. The present method involves the monitoring of known or presumed capacitance values between cells to determine if imperfections exist. The primary problem with this method, however, is that cell capacitance tends to vary over a wide range due to the variation in distance between anode and cathode in the stacked cells due to variation in the effective cell compression. This, of course, makes the method conductive fibers which may be unreliable. Another method is to attach a small lead wire to each collector plate to measure internal cell resistance. This approach is not always possible due to space limitations within the stacked construction together with increased intercell leakage due to a plurality of exposed lead wires. Thus, there remains a definite need to provide a simple yet reliable method of monitoring the quality control in multi-layer, stacked, bipolar battery construction.